Fastening arrangement for plastics handles of scissors and equivalent

ABSTRACT

A fastening arrangement for plastics handles of scissors and equivalent in constructions in which the plastics handle is die-cast around a tang at the end of the blade-shaft. The tang has such a generally curved shape that on the outside of the blade-shaft there will be a rather thick plastics layer at the end of the tang, and, correspondingly, on the inside of the blade-shaft there will be a rather thick plastics layer at the root end of the tang.

The present invention concerns a fastening arrangement for plasticshandles in cutting tools, such as scissors and pliers, comprising twoblade-shafts pivotably fastened to each other, the handles beingdie-cast around the end portion of the blade-shafts, the arrangementcomprising a tang forming said end portion of each blade-shaft andhaving such a generally curved shape.

In scissors of this type, the plastics handles are die-cast in a mouldaround a tang at the end of the blade-shaft. Previously, an arrangementwas used in which the joint was approximately symmetrical in relation tothe longitudinal axis of the blade shaft. A drawback with thisarrangement was that handles were broken in heavy use.

BRIEF DESCRIPTION OF THE DRAWINGS.

FIG. 1 shows an earlier fastening arrangement, partly in section.

FIGS. 1A and 1B are cross sections taken at A--A and B--B of FIG. 1.

FIG. 2 shows another earlier fastening arrangement, partly in section.

FIG. 3 shows one embodiment of the fastening arrangement in accordancewith the invention, partly in section.

FIGS. 3A and 3B are cross sections taken at A--A and B--B of FIG. 3.

FIG. 4 shows another embodiment of the fastening arrangement inaccordance with the invention, partly in section.

To begin with, let us have a somewhat closer look at the earliersolution of said type. Such a solution is presented in FIGS. 1 and 2 ofthe attached drawings, which show a commonly used fastening arrangement,partly in section. Here, the fastening of both handles 1 of the scissorhalves to the blade-shaft 2 is accomplished by using an almost similarsymmetric tang 3. This tang is expanded at its outer end so as toimprove the holding quality. During shearing, the effective force actsin the direction of the arrow F. Then, at the section A--A, bendingarises, but so that a tensile force is produced only above the tang 3(FIG. 1). The end of the tang 3 is expanded so much that the plasticslayer at this point is quite thin. In this case, for example at points 5and 6, a high tension is produced (section B--B).

The object of the present invention is to eliminate the drawbackpresented above and to provide a fastening arrangement of a novel type.

The fastening arrangement in accordance with the invention is mainlycharacterized in that on the outside of the blade-shaft there will be arather thick plastics layer at the outer end of the tang, and,correspondingly, on the inside of the blade-shaft there will be a ratherthick plastics layer at the root end of the tang.

Particular embodiments of the fastening arrangement in accordance withthe invention are defined in claims 2 to 5.

By means of the invention, remarkable advantages are obtained. Thus, thearrangement produces a remarkable improvement in the firmness of thejoint between the plastics and the blade-shaft. In fact, with staticloading, the new solution does not display a major difference instrength as compared with the earlier solution. Both the old and the newsolution stand a load of 70 to 80 kg under the same circumstances. But,on the contrary, when the handles are loaded dynamically, as is done innormal use, the difference is, however, considerable. For example, ifthe load is 20 kg and the frequency 3 cycles per second, it has beenestablished that the ratio of the times of durability is about 10 to 1in favour of the new solution. When the load is reduced, this ratiobecomes even higher. It should be mentioned that when shearing withscissors, the maximum force attainable is about 15 kg.

The invention will be examined below in more detail, reference beingmade to FIGS. 3 and 4 in the attached drawings.

FIG. 3 shows one embodiment of the fastening arrangement in accordancewith the invention, partly in section.

FIG. 4 shows another embodiment of the fastening arrangement inaccordance with the invention, partly in section.

As the solutions of FIG. 3 and FIG. 4 are highly similar and as theycan, moreover, be included in the same construction of scissors, theywill be described below simultaneously. The tang 3 has such anasymmetric design that it is, in principle, curved whereby the concaveside 4 of the curve points in the direction of the force F. Thus, on theother, convex side of the tang 3, a layer of plastics 10 is left overwhose thickness varies so that at the outer end 7,8 of the tang 3 thereis a maximum quantity of plastics in the direction of the force F. Whenmoving along the outer edge of the blade-shaft 2 outwards, the outerside of the tang 3 becomes almost evenly more distant from the directionof the outer edge of the blade-shaft 2 so that the layer 10 of plasticslying against the outer side 3 of the tang is in this example caseapproximately triangular as to its shape.

Correspondingly, at the position of the tang 3 where the plastics of thehandle 1 ends, there is a notch 4 opening in the direction of the forceF so that at the inner edge of the blade-shaft 2 of the scissors, i.e.relatively close to the pivot axis 12 of the scissors, there is a ratherthick layer 9 of plastics. On the contrary, closer to the outer end 7,8of the tang 3, the thickness 11 of the plastics at the inner edge of theblade-shaft 2 may be quite thin.

The cross-section of the notch 4 may, in principle, be of severaldifferent shapes, e.g. V or U shaped, angular or polygonal. However, thesemicircular notch 4 as shown in FIGS. 3 and 4 provides the advantagethat it is production-technically the most advantageous one, forexample, when the blanks are cut (circular punch), when the objects arefastened at the different stages of production, and when the plastics isdie-cast. For, during die-casting, the casting position is placed sothat the plastics jet meets the bottom of the notch and that the fillingof the mould takes place in a favourable manner. For, as regards theresistance to fatigue of plastics, the direction of the molecular chainshas a great significance.

The solution of FIG. 3 differs from that of FIG. 4, in principle, onlyin the respect that in the former solution, owing to the small size ofthe loop portion of the handle 1, the tang 3 may extend axially as alengthy tip 7 into the plastics, whereas in the latter case the tip ofthe tang 3 is cut and designed as a hook-shaped nose 8.

By shaping the tang in accordance with the principles presented above,it has been possible to place a large quantity of plastics at thepositions at which the effective shear forces are largest, and theincrease in the resistance to dynamic strain is even surprisingly high.

It is clear that the solution in accordance with the invention can,besides scissors, be used, for example, in garden scissors, pliers andother similar tools in which plastics handles are at their fasteningpoints subjected to relatively high shear forces.

I claim:
 1. A fastening arrangement for plastics handles in cuttingtools, such as scissors and pliers, comprising two blade-shaftspivotably fastened to each other, the handles being die-cast around theend portion of the blade-shafts, the arrangement comprising a tangforming said end portion of each blade-shaft and formed at its root endwith a notch at the inner edge of the blade-shaft, which notch is filledwith plastics to procide a relatively thick plastics layer on the insideof the blade-shaft at the root end of the tang, and said tang beinggenerally curved so that the surface of the tang at the outer edge ofthe blade-shaft becomes progressively more distant from the direction ofsaid outer edge so as to provide an approximately triangular plasticslayer on the outside of the tang, said triangular plastics layer beingof greater thickness at the outer end of the tang than at the root endthereof.
 2. A fastening arrangement as claimed in claim 1, wherein thecross-section of the notch is of a semicircular shape.